NEA set for field test of mosquitoes infected with bacteria

Female mosquito, Aedes aegypti species.
Female mosquito, Aedes aegypti species. ST PHOTO: LIM SIN THAI

Trial will see if infected males will mate with females in wild to make eggs that don't hatch

Male mosquitoes infected with bacteria called Wolbachia have proven their worth in the lab.

They are fit enough to mate with female mosquitoes, causing them to lay eggs which do not hatch. The bacteria can also be successfully passed down from Wolbachia- infected female mosquitoes to their offspring.

All that is left for researchers now is to test how well they perform in the field, said Dr Ng Lee Ching, director of the National Environment Agency's (NEA) Environmental Health Institute.

"We have done all we can in the lab," Dr Ng told The Straits Times.

"But we are never sure that it (behaves) exactly the same way in the field," she added.

In April, the Government announced that Singapore would be conducting a small-scale field study and releasing male Aedes aegypti mosquitoes infected with Wolbachia.

This is to test if these mosquitoes can be a weapon against dengue.

No other details were provided except that the aim of the study would be to find out the insects' behaviour, such as longevity and flight range, in a built-up environment.

ACCURATE MEASUREMENT

Keep in mind though, laboratory experimental data may not reflect what happens in nature. An active enhanced surveillance system needs to be put in place to accurately measure the effect on dengue transmission.

EMERITUS PROFESSOR DUANE GUBLER, from the Duke-NUS Medical School.

"The whole idea is to release male mosquitoes to hunt for females," said Dr Ng.

"So how fit is it? Is it able to fly up to hunt for females at the top level? We don't know. That's why all these studies have to be done in the field."

Wolbachia-infected mosquitoes are able to survive for one month in the lab but Dr Ng says it is not known for how long they would last in the wild, although she suspects the lifespan would be shorter.

The results of the field study would help them to know how many insects have to be released in order be effective.

When male mosquitoes carrying the bacteria mate with wild female mosquitoes, they produce eggs that do not hatch. In the long run, releasing these mosquitoes could help to suppress the number of Aedes aegypti mosquitoes - the main carriers of dengue, Zika and chikungunya.

Based on the NEA's assessment so far, the technology poses no or insignificant risk of negative impact on public health or the ecosystem.

Testing out the Wolbachia technology is part of Singapore's search for new ways to minimise dengue risk.

The authorities had warned earlier that the number of dengue cases this year may exceed 30,000 - higher than the record in 2013, when 22,170 cases were reported.

Last month, the NEA said that close to 9,000 dengue cases had been reported as of June 25. This is more than twice the number in the same period last year.

Current methods alone are no longer sufficient to tackle dengue, based on the outbreaks that Singapore has had, says Dr Ng.

Despite having a relatively low population of mosquitoes, Singapore still suffers from dengue outbreaks, she noted.

"We also have some cryptic sites. Sometimes you can't find the mosquitoes. They might be there but you just can't find them."

According to the NEA, $72 million was spent on dengue in the 2014-2015 financial year. The money went to various areas such as research, public education and elimination of mosquito breeding.

Singapore will not be the first to use Wolbachia technology to combat the threat of dengue. Other countries such as China and the United States have released male mosquitoes infected with Wolbachia.

Over in California in the US, for instance, trials by biotech company MosquitoMate started last month and will continue through October. A total of 40,000 mosquitoes are released in 20 sites each week.

World renowned dengue expert Duane Gubler, an emeritus professor from the Duke-NUS Medical School, said that based on experimental data, the Wolbachia-carrying male mosquitoes should be effective in suppressing the Aedes aegypti, even in a "built-up environment like Singapore".

"Keep in mind though, laboratory experimental data may not reflect what happens in nature. An active enhanced surveillance system needs to be put in place to accurately measure the effect on dengue transmission," he added.

A version of this article appeared in the print edition of The Straits Times on July 29, 2016, with the headline 'NEA set for field test of mosquitoes infected with bacteria'. Print Edition | Subscribe